Conductive polymer materials are used for electrodes of capacitors, electrodes of dye-sensitized solar cells and the like, electrodes of electroluminescence displays, etc. As such conductive polymer materials, conductive polymers are known which are obtained by the polymerization of pyrrole, thiophene, aniline, etc.
These types of conductive polymers are typically provided as dispersion liquids (suspensions) or solutions in aqueous solvents, or as solutions using organic solvents. The solvents are removed before use as conductive polymer materials. Even in the case of the same type of conductive polymer, the physical properties of obtained conductive polymer materials vary depending on the conditions of the dispersion liquid. Thus, various studies have been carried out on methods for producing dispersion liquids.
PTL 1 discloses a technique which relates to a solution (dispersion liquid) of polythiophene and a method for producing the solution, as well as the use of the solution for antistatic treatment of plastic compacts. This dispersion of polythiophene contains: water or a mixture of a water-miscible organic solvent and water as a dispersion medium; polythiophene composed of structural units of 3,4-dialkoxythiophene; and polyanions derived from a polystyrene sulfonic acid having a molecular weight in the range of 2,000 to 500,000. Further, the polythiophene is obtained by chemical oxidative polymerization in the presence of the polystyrene sulfonic acid (polyanions) having a molecular weight in the range of 2,000 to 500,000. Thus, transparent antistatic films can be formed.
PTL 2 discloses a technique which relates to a conductive composition containing a π-conjugated conductive polymer, a dopant, and a nitrogen-containing aromatic cyclic compound, and to a conductive cross-linked product formed by applying a heat treatment and/or an ultraviolet irradiation treatment to the conductive composition. For example, 3,4-ethylenedioxythiophene is polymerized in an aqueous solvent with the use of an oxidant in the presence of a polystyrene sulfonic acid (polanions). Thus, formed is a water dispersion of a composite of poly(3,4-ethylenedioxythiophene) and the polystyrene sulfonic acid. Then, a conductive composition is obtained by adding a nitrogen-containing aromatic cyclic compound containing imidazole to the water dispersion.
In addition, PTL 3 discloses a solid electrolytic capacitor using a conductive polymer dispersion liquid. The solid electrolytic capacitor has a cathode formed from the conductive polymer dispersion liquid. The conductive polymer dispersion liquid contains: conductive particles composed of a π-conjugated conductive polymer and a solubilized polymer; and a solvent, and contains 50 volume % or more of conductive particles of 5 nm to 100 nm in particle size. The mass average molecular weight of the solubilized polymer from 1,000 to 300,000 increases the permeability into a porous body, thereby making it possible to efficiently extract the capacitance of a capacitor.